The present invention relates to an improved wire pull back delivery system. More specifically, the invention relates to a wire pull-back stent delivery system which utilizes a shape memory contraction member to retract the retractable outer sheath and deploy a medical implant for a minimally invasive application, such as an endovascular stent graft, vena cava filter, aneurysm repair particles, self-expanding stent, balloon expandable stent, or the like.
Delivery systems for deploying medical implants, such as an endovascular stent graft, vena cava filter, self-expanding stent, balloon expandable stent or the like, are a highly developed and well known field of medical technology. These medical devices have many well known uses and applications. In particular, a stent is a prosthesis which is generally tubular and which is expanded radially in a vessel or lumen to maintain its patency. Stents are widely used in body vessels, body canals, ducts or other body lumens. Balloon expandable stents are mounted on a balloon which when expanded delivers the stent, exerting radial force on the constricted portion of the body lumen to re-establish patency. A self-expanding stent is a stent which expands from a compressed delivery position to its original diameter when released from the delivery device, exerting radial force on the constricted portion of the body lumen to re-establish patency. One common self-expanding stent is manufactured of Nitinol, a nickel-titanium shape memory alloy, which can be formed and annealed, deformed at a low temperature, and recalled to its original shape with heating, such as when deployed at body temperature in the body. A common material for balloon expandable stents is stainless steel.
Wire pull-back stent delivery systems commonly assigned with this application include U.S. Pat. No. 5,571,135, U.S. Ser. No. 08/753,641 filed Sep. 27, 1996 and U.S. Pat. No. 5,733,267, the entire contents of which are hereby incorporated by reference. Another wire pull-back stent delivery system is shown in U.S. Pat. No. 5,360,401. One important factor in delivering the stent is a controlled precise retraction of the retractable outer sheath. What is needed is a wire pull-back stent delivery system which provides for a controlled and precise retraction of the retractable outer sheath and enables the physician to accurately determine proper positioning of the stent.